Various stable voltages are generally needed in electronic circuits. In order to be able to supply these various voltage levels, there are used, among others, voltage regulators. Voltage regulators, which operate in systems with high battery voltage VBAT and a DC/DC buck-converter, are normally supplied with an output voltage VDCDC of the buck-converter, in order to keep power loss low in the voltage regulator. Such voltage regulators are used e.g. in motor vehicles, in order to supply a regulated supply voltage to electric control devices such as e.g. microcontrollers and other critical components. The requirements regarding the output voltage of the voltage regulator are high.
For supplying a voltage regulator in a motor vehicle the generally higher battery voltage VBAT, which in a motor vehicle can be overlaid by high positive and negative parasitic voltages, is converted by the buck-converter into a comparatively lower intermediate potential VDCDC. The power dissipation in the voltage regulator is thus maintained low. In order to regulate the output voltage of the voltage regulator, e.g. a regulation transistor incorporated into a regulation circuit can suitably be connected between the intermediate potential VDCDC and the output voltage of the voltage regulator, which regulates the voltage drop between VDCDC and the output by means of an applied control potential. If the battery voltage VBAT drops, the output voltage of the buck-converter VDCDC at first remains constant and starts to drop according to VBAT as soon as VBAT drops to a saturation voltage above the set value of VDCDC. In order to allow the voltage regulator to operate even when the battery voltage drops further and, hence, at intermediate voltages VDCDC set to a lower value dropping to the same extent, a bypass transistor can in this case be connected to the regulation transistor of the voltage regulator.
Abrupt connecting, however, causes unwanted voltage peaks or voltage dips (so-called glitches) at the output of the voltage regulator. These glitches can e.g. cause short-duration false assertions in logic circuits supplied with the regulated voltage and are thus a substantial problem for the development of modern electronic circuits. E.g. in the field of the motor vehicles, glitches are therefore unacceptable, since they could cause failures of the control electronics.